Because obesity is very prevalent, results in marked morbidity and mortality, and is treatment resistant, it is vital to develop prevention programs for this public health problem. Unfortunately, virtually all prevention programs have not reduced risk for future weight gain. We developed a selected prevention program that targets the 50 percent of female adolescents with the highest body dissatisfaction because a preliminary study indicated that they have an 8-fold increased risk for obesity onset over a 4-year follow-up relative to those below this cut-off. In the Healthy Weight program, female adolescents with body image concerns are encouraged to reduce caloric intake and to increase physical activity as a way of improving body satisfaction. This intervention uses persuasion principles from social and clinical psychology (e.g., strategic self-presentation, motivational enhancement techniques) to increase the likelihood that participants will make lasting behavioral changes. It is very brief (3 hrs) relative to extant programs (M = 43 hrs), which should facilitate dissemination. A preliminary trial (N = 188) found that participants who completed the Healthy Weight program were at significantly lower risk for obesity onset over a 2-year follow-up (3 percent) than assessment-only controls (12 percent) and showed greater improvements in healthy eating and physical activity. This program also reduced eating disorder symptoms and negative affect, which is important because these disturbances result in functional impairment and adverse outcomes. We propose to conduct a large randomized trial of an enhanced version of this obesity prevention program. We will randomly assign 405 female adolescents (aged 17-19) with body image concerns from a local college to the Healthy Weight intervention or a psychoeducational control condition and follow them for 2 years. We will test whether the Healthy Weight program, relative to the control intervention, results in (1) decreased risk for obesity onset and increased weight, (2) decreased caloric intake and increased physical activity, and (3) decreased body dissatisfaction, bulimic symptoms, and depressive symptoms. We will also (4) test whether changes in caloric intake and activity level mediate intervention effects on weight gain prevention and (5) investigate potential moderators of intervention effects. The use of random assignment, an attention control condition, blinded diagnostic interviews, and a long-term follow-up make the proposed trial more rigorous than past trials. We will also validate key measures in a subgroup of participants with objective measures (e.g., doubly-labeled water and accelerometers). The development of an effective obesity prevention program that can be easily and inexpensively disseminated could substantially reduce the rate of obesity and resulting morbidity and mortality. The fact that this intervention also produces effects for eating disorder symptoms and depression further increases the public health relevance of the proposed trial.